1. Field of the Invention
This invention relates to a computer game system utilizing video and music, and more particularly to a technique of recording and reproducing video and music in the computer game system.
2. Description of Related Art
There are known various games incorporating essence of music. In one of such games, a game player (user) operates an input device in conformity with music reproduced by the game system and/or marks shown on a display monitor of the game. In a game of another type, the game players are given a guidance of how to dance and compete with each other by their scores indicating how well they danced. Recently, compressive encoding technique of video data, such as MPEG2 system, is applied to such music game systems in order to enhance the quality of game picture.
The compressive encoding technique such as MPEG2 system compresses video data utilizing correlation of successive pictures in the time axis, and hence it is necessary to decode the video data by every predetermined unit to reproduce the video data. Specifically, in the case of MPEG2, the video data is decoded and reproduced by the data unit called GOP (Group Of Picture).
On the other hand, the video data constituted by a group of GOPs is recorded on a storage medium by the unit of the sector formed on the storage medium, and hence the video data including a plurality of successive GOPs according to the MPEG2 system is recorded on a plurality of sectors. At this time, the GOPs are not positioned correspondingly with the positions of the sectors.
At the time of reproduction, the video data recorded on the successive sectors are temporarily stored into the buffer memory, and the GOPs are identified and extracted from the video data of the plural sectors. Then, the video data is supplied from the buffer memory to the decoder by the unit of GOP, and then the decoding processing is performed.
However, in such a music game, the game player not only simply reproduces the tune from its start to its end, but also controls the reproduction of the tune by changing the reproduction position to the intermediate portion of the tune or another tune, or by repeatedly reproducing the same portion of the tune, thereby to enjoy playing the game. In such a case, the read-out position of the video data is changed according to the change of the reproduction position. However, as mentioned above, the video data can be reproduced only by the GOP unit and the head of the sector does not necessarily coincide with the head of the GOP. Therefore, every time when the reproduction position is changed, the video data of several sectors around the reproduction position after the change is stored into the buffer memory and the GOP unit is identified to decode the video data. This process is quite complicated, and requires a buffer memory of large storage capacity. In addition, since this process lowers the processing speed, it is inappropriate that the game system executes this process on the real-time basis during the game play.